High-glucose diets have sex-specific effects on aging in C. elegans: toxic to hermaphrodites but beneficial to males

Glucose-fed microbiota alters C. elegans intestinal epithelium and increases susceptibility to multiple bacterial pathogens

Overconsumption of dietary sugar can lead to many negative health effects including the development of Type 2 diabetes, metabolic syndrome, cardiovascular disease, and neurodegenerative disorders. Recently, the human intestinal microbiota, strongly associated with our overall health, has also been known to be affected by diet. However, mechanistic insight into the importance of the human intestinal microbiota and the effects of chronic sugar ingestion has not been possible largely due to the complexity of the human microbiome which contains hundreds of types of organisms. Here, we use an interspecies C. elegans/E. coli system, where E. coli are subjected to high sugar, then consumed by the bacterivore host C. elegans to become the microbiota. This glucose-fed microbiota results in a significant lifespan reduction accompanied by reduced healthspan (locomotion), reduced stress resistance, and changes in behavior and feeding. Lifespan reduction is also accompanied by two potential major contributors: increased intestinal bacterial density and increased concentration of reactive oxygen species. The glucose-fed microbiota accelerated the age-related development of intestinal cell permeability, intestinal distention, and dysregulation of immune effectors. Ultimately, the changes in the intestinal epithelium due to aging with the glucose-fed microbiota results in increased susceptibility to multiple bacterial pathogens. Taken together, our data reveal that chronic ingestion of sugar, such as a Western diet, has profound health effects on the host due to changes in the microbiota and may contribute to the current increased incidence of ailments including inflammatory bowel diseases as well as multiple age-related diseases.

Lack of detectable sex differences in the mitochondrial function of Caenorhabditis elegans

BACKGROUND

Sex differences in mitochondrial function have been reported in multiple tissue and cell types. Additionally, sex-variable responses to stressors including environmental pollutants and drugs that cause mitochondrial toxicity have been observed. The mechanisms that establish these differences are thought to include hormonal modulation, epigenetic regulation, double dosing of X-linked genes, and the maternal inheritance of mtDNA. Understanding the drivers of sex differences in mitochondrial function and being able to model them in vitro is important for identifying toxic compounds with sex-variable effects. Additionally, understanding how sex differences in mitochondrial function compare across species may permit insight into the drivers of these differences, which is important for basic biology research. This study explored whether Caenorhabditis elegans, a model organism commonly used to study stress biology and toxicology, exhibits sex differences in mitochondrial function and toxicant susceptibility. To assess sex differences in mitochondrial function, we utilized four male enriched populations (N2 wild-type male enriched, fog-2(q71), him-5(e1490), and him-8(e1498)). We performed whole worm respirometry and determined whole worm ATP levels and mtDNA copy number. To probe whether sex differences manifest only after stress and inform the growing use of C. elegans as a mitochondrial health and toxicologic model, we also assessed susceptibility to a classic mitochondrial toxicant, rotenone.

RESULTS

We detected few to no large differences in mitochondrial function between C. elegans sexes. Though we saw no sex differences in vulnerability to rotenone, we did observe sex differences in the uptake of this lipophilic compound, which may be of interest to those utilizing C. elegans as a model organism for toxicologic studies. Additionally, we observed altered non-mitochondrial respiration in two him strains, which may be of interest to other researchers utilizing these strains.

CONCLUSIONS

Basal mitochondrial parameters in male and hermaphrodite C. elegans are similar, at least at the whole-organism level, as is toxicity associated with a mitochondrial Complex I inhibitor, rotenone. Our data highlights the limitation of using C. elegans as a model to study sex-variable mitochondrial function and toxicological responses.

Chronic high-sugar diet in adulthood protects Caenorhabditis elegans from 6-OHDA-induced dopaminergic neurodegeneration

BACKGROUND

Diets high in saturated fat and sugar, termed "Western diets," have been associated with several negative health outcomes, including increased risk for neurodegenerative disease. Parkinson's disease (PD) is the second most prevalent neurodegenerative disease and is characterized by the progressive death of dopaminergic neurons in the brain. We build upon previous work characterizing the impact of high-sugar diets in Caenorhabditis elegans to mechanistically evaluate the relationship between high-sugar diets and dopaminergic neurodegeneration.

RESULTS

Adult high-glucose and high-fructose diets, or exposure from day 1 to 5 of adulthood, led to increased lipid content, shorter lifespan, and decreased reproduction. However, in contrast to previous reports, we found that adult chronic high-glucose and high-fructose diets did not induce dopaminergic neurodegeneration alone and were protective from 6-hydroxydopamine (6-OHDA) induced degeneration. Neither sugar altered baseline electron transport chain function and both increased vulnerability to organism-wide ATP depletion when the electron transport chain was inhibited, arguing against energetic rescue as a basis for neuroprotection. The induction of oxidative stress by 6-OHDA is hypothesized to contribute to its pathology, and high-sugar diets prevented this increase in the soma of the dopaminergic neurons. However, we did not find increased expression of antioxidant enzymes or glutathione levels. Instead, we found evidence suggesting downregulation of the dopamine reuptake transporter dat-1 that could result in decreased 6-OHDA uptake.

CONCLUSIONS

Our work uncovers a neuroprotective role for high-sugar diets, despite concomitant decreases in lifespan and reproduction. Our results support the broader finding that ATP depletion alone is insufficient to induce dopaminergic neurodegeneration, whereas increased neuronal oxidative stress may drive degeneration. Finally, our work highlights the importance of evaluating lifestyle by toxicant interactions.

Novel studies on Drosophila melanogaster model reveal the roles of JNK-Jak/STAT axis and intestinal microbiota in insulin resistance

The JNK pathway play a critical role in insulin resistance induced by a long-term high-sugar diet. However, the roles of up- and downstream molecules of the JNK pathway in insulin resistance are less known in vertebrates and invertebrates. As a classical organism in biological research, Drosophila melanogaster (D. melanogaster) has been widely applied to the studies of mechanism of insulin resistance. Based on previous studies, we found a novel predictive mechanism of the formation of insulin resistance in D. melanogaster. We found that JNK activated by high-sugar diet and dysregulated intestinal microbiota could mediate inflammation, and then the activated JNK released Upd3, which in turn stimulated Jak/STAT pathway to release ImpL2. ImpL2 can compete with Drosophila insulin-like peptides (Dilps) for binding with the insulin receptor and inhibit the activation of insulin pathway. In this study, we reviewed novel studies on the insulin signalling pathway based on the D. melanogaster model. The findings support our hypothesis. We, therefore, described how a long-term high-sugar diet disrupts intestinal microbiota to induce inflammation and the disruption of JNK-Jak/STAT axis. This description may offer some new clues to the formation of insulin resistance.

Sex-specificity of the C. elegans metabolome

Recent studies of animal metabolism have revealed large numbers of novel metabolites that are involved in all aspects of organismal biology, but it is unclear to what extent metabolomes differ between sexes. Here, using untargeted comparative metabolomics for the analysis of wildtype animals and sex determination mutants, we show that C. elegans hermaphrodites and males exhibit pervasive metabolomic differences. Several hundred small molecules are produced exclusively or in much larger amounts in one sex, including a host of previously unreported metabolites that incorporate building blocks from nucleoside, carbohydrate, lipid, and amino acid metabolism. A subset of male-enriched metabolites is specifically associated with the presence of a male germline, whereas enrichment of other compounds requires a male soma. Further, we show that one of the male germline-dependent metabolites, an unusual dipeptide incorporating N,N-dimethyltryptophan, increases food consumption, reduces lifespan, and accelerates the last stage of larval development in hermaphrodites. Our results serve as a foundation for mechanistic studies of how the genetic sex of soma and germline shape the C. elegans metabolome and provide a blueprint for the discovery of sex-dependent metabolites in other animals.

The unfolded protein response reverses the effects of glucose on lifespan in chemically-sterilized C. elegans

Metabolic diseases often share common traits, including accumulation of unfolded proteins in the endoplasmic reticulum (ER). Upon ER stress, the unfolded protein response (UPR) is activated to limit cellular damage which weakens with age. Here, we show that Caenorhabditis elegans fed a bacterial diet supplemented high glucose at day 5 of adulthood (HGD-5) extends their lifespan, whereas exposed at day 1 (HGD-1) experience shortened longevity. We observed a metabolic shift only in HGD-1, while glucose and infertility synergistically prolonged the lifespan of HGD-5, independently of DAF-16. Notably, we identified that UPR stress sensors ATF-6 and PEK-1 contributed to the longevity of HGD-5 worms, while ire-1 ablation drastically increased HGD-1 lifespan. Together, we postulate that HGD activates the otherwise quiescent UPR in aged worms to overcome ageing-related stress and restore ER homeostasis. In contrast, young animals subjected to HGD provokes unresolved ER stress, conversely leading to a detrimental stress response.

Caenorhabditis elegans as an emerging model in food and nutrition research: importance of standardizing base diet

As a model organism that has helped revolutionize life sciences, Caenorhabditis elegans has been increasingly used in nutrition research. Here we explore the tradeoffs between pros and cons of its use as a dietary model based primarily on literature review from the past decade. We first provide an overview of its experimental strengths as an animal model, focusing on lifespan and healthspan, behavioral and physiological phenotypes, and conservation of key nutritional pathways. We then summarize recent advances of its use in nutritional studies, e.g. food preference and feeding behavior, sugar status and metabolic reprogramming, lifetime and transgenerational nutrition tracking, and diet-microbiota-host interactions, highlighting cutting-edge technologies originated from or developed in C. elegans. We further review current challenges of using C. elegans as a nutritional model, followed by in-depth discussions on potential solutions. In particular, growth scales and throughputs, food uptake mode, and axenic culture of C. elegans are appraised in the context of food research. We also provide perspectives for future development of chemically defined nematode food ("NemaFood") for C. elegans, which is now widely accepted as a versatile and affordable in vivo model and has begun to show transformative potential to pioneer nutrition science.

High-Glucose Diet Attenuates the Dopaminergic Neuronal Function in C. elegans, Leading to the Acceleration of the Aging Process

Parkinson's disease (PD) is a neurodegenerative disease characterized by the selective degeneration of neurons, primarily in the substantia nigra. Environmental or exogenous factors that cause Parkinson's disease have not been sufficiently elucidated. Our study aims to investigate the causative effect of a high-glucose diet on Parkinson's disease-relevant dopaminergic neuronal system in Caenorhabditis elegans. Aging parameters were first observed by measuring the lifespan, body movement, and body sizes with and without the background of high glucose. The toxic effect of a high-glucose diet was further explored by observing the dopaminergic neurons using transgenic Pdat-1::gfp strains, BZ555, under a Zeiss microscope, and the experiments were extended by assessing dopamine-related behavioral analysis including basal slowing response and alcohol avoidance. The aggregation of the α-synucleins was also assessed by observing the NL5901 mutants. Worms fed with 250 mM glucose showed daf-2-independent regulation of aging, displaying a short lifespan (≤15 days), long body size (max. 140%), and slow movement (min. 30%, 10 bends/min). Anterior dopaminergic neurons were rapidly inactivated (70%) by a glucose-rich diet from 12 h of exposure, suggesting specific degeneration in ADE neurons. The dysregulation of neurons led to deteriorations in dopaminergic behaviors including basal slowing response (BSR). A high-glucose diet decreased dopamine synthesis (40 pg/mg vs 15 pg/mg protein) and induced α-synuclein aggregation in the muscles. Results demonstrate the potential of a high-glucose diet as a trigger of dopaminergic neuronal dysregulation conjugating aging acceleration.

The symbiotic relationship between Caenorhabditis elegans and members of its microbiome contributes to worm fitness and lifespan extension

Background

A healthy microbiome influences host physiology through a mutualistic relationship, which can be important for the host to cope with cellular stress by promoting fitness and survival. The mammalian microbiome is highly complex and attributing host phenotypes to a specific member of the microbiome can be difficult. The model organism Caenorhabditis elegans and its native microbiome, discovered recently, can serve as a more tractable, experimental model system to study host-microbiome interactions. In this study, we investigated whether certain members of C. elegans native microbiome would offer a benefit to their host and putative molecular mechanisms using a combination of phenotype screening, omics profiling and functional validation.

Results

A total of 16 members of C. elegans microbiome were screened under chemically-induced toxicity. Worms grown with Chryseobacterium sp. CHNTR56 MYb120 or Comamonas sp. 12022 MYb131, were most resistant to oxidative chemical stress (SiO₂ nanoparticles and juglone), as measured by progeny output. Further investigation showed that Chryseobacterium sp. CHNTR56 positively influenced the worm’s lifespan, whereas the combination of both isolates had a synergistic effect. RNAseq analysis of young adult worms, grown with either isolate, revealed the enrichment of cellular detoxification mechanisms (glutathione metabolism, drug metabolism and metabolism of xenobiotics) and signaling pathways (TGF-beta and Wnt signaling pathways). Upregulation of cysteine synthases (cysl genes) in the worms, associated with glutathione metabolism, was also observed. Nanopore sequencing uncovered that the genomes of the two isolates have evolved to favor the specific route of the de novo synthesis pathway of vitamin B6 (cofactor of cysl enzymes) through serC or pdxA2 homologs. Finally, co-culture with vitamin B6 extended worm lifespan.

Conclusions

In summary, our study indicates that certain colonizing members of C. elegans have genomic diversity in vitamin B6 synthesis and promote host fitness and lifespan extension. The regulation of host cellular detoxification genes (i.e. gst) along with cysl genes at the transcriptome level and the bacterium-specific vitamin B6 synthesis mechanism at the genome level are in an agreement with enhanced host glutathione-based cellular detoxification due to this interspecies relationship. C. elegans is therefore a promising alternative model to study host-microbiome interactions in host fitness and lifespan.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07695-y.

Bacterial processing of glucose modulates C. elegans lifespan and healthspan

Intestinal microbiota play an essential role in the health of a host organism. Here, we define how commensal Escherichia coli (E. coli) alters its host after long term exposure to glucose using a Caenorhabditis elegans-E. coli system where only the bacteria have direct contact with glucose. Our data reveal that bacterial processing of glucose results in reduced lifespan and healthspan including reduced locomotion, oxidative stress resistance, and heat stress resistance in C. elegans. With chronic exposure to glucose, E. coli exhibits growth defects and increased advanced glycation end products. These negative effects are abrogated when the E. coli is not able to process the additional glucose and by the addition of the anti-glycation compound carnosine. Physiological changes of the host C. elegans are accompanied by dysregulation of detoxifying genes including glyoxalase, glutathione-S-transferase, and superoxide dismutase. Loss of the glutathione-S-transferase, gst-4 shortens C. elegans lifespan and blunts the animal's response to a glucose fed bacterial diet. Taken together, we reveal that added dietary sugar may alter intestinal microbial E. coli to decrease lifespan and healthspan of the host and define a critical role of detoxification genes in maintaining health during a chronic high-sugar diet.

Protective effects of black bamboo leaves on the glucose-induced toxicity in Caenorhabditis elegans

Introduction: Previous studies have suggested that high glucose (HG) condition shortens the lifespan of worms by increasing glycolytic flux followed by accelerating reactive oxygen species (ROS) production, termed glucose toxicity. This study was designed to investigate the protective effects of the leaves of black bamboo (Phyllostachys nigra var. henosis) on the HG-induced toxicity using Caenorhabditis elegans model system. Methods: To determine the effect of black bamboo leaf extract (BLE) against HG-induced toxicity, lifespan assay was carried out with wild-type and daf-16 null mutant worms under 2% glucose condition. The involvement of DAF-16 was further confirmed by observing fluorescence signal of transgenic mutant carrying DAF-16::GFP transgene. ROS levels and glucose concentration of worms were analyzed using fluorescent probe H2DCF-DA and glucose meter, respectively. Nile-red staining was carried out to evaluate the lipid storage of worms. Intercellular lipid accumulation was measured using Oil-Red O staining method. Results: BLE strongly extended the lifespan of worms under not only normal culture condition but also HG condition. Our additional studies suggested that DAF-16 activation was responsible for BLE-mediated longevity and protective action against glucose toxicity. In addition, HG-fed worms showed increased ROS generation, and it was completely normalized by BLE treatment. Moreover, BLE reduced body glucose concentration and lipid accumulation in HG-fed worms. We further confirmed the inhibitory effect of BLE on lipid storage under HG condition using 3T3-L1 adipocytes. Conclusion: These therapeutic values of BLE on glucose toxicity raise the possibility that BLE might have beneficial effects on the pathogenesis of diabetes mellitus.

Gluconeogenesis and PEPCK are critical components of healthy aging and dietary restriction life extension

High glucose diets are unhealthy, although the mechanisms by which elevated glucose is harmful to whole animal physiology are not well understood. In Caenorhabditis elegans, high glucose shortens lifespan, while chemically inflicted glucose restriction promotes longevity. We investigated the impact of glucose metabolism on aging quality (maintained locomotory capacity and median lifespan) and found that, in addition to shortening lifespan, excess glucose negatively impacts locomotory healthspan. Conversely, disrupting glucose utilization by knockdown of glycolysis-specific genes results in large mid-age physical improvements via a mechanism that requires the FOXO transcription factor DAF-16. Adult locomotory capacity is extended by glycolysis disruption, but maximum lifespan is not, indicating that limiting glycolysis can increase the proportion of life spent in mobility health. We also considered the largely ignored role of glucose biosynthesis (gluconeogenesis) in adult health. Directed perturbations of gluconeogenic genes that specify single direction enzymatic reactions for glucose synthesis decrease locomotory healthspan, suggesting that gluconeogenesis is needed for healthy aging. Consistent with this idea, overexpression of the central gluconeogenic gene pck-2 (encoding PEPCK) increases health measures via a mechanism that requires DAF-16 to promote pck-2 expression in specific intestinal cells. Dietary restriction also features DAF-16-dependent pck-2 expression in the intestine, and the healthspan benefits conferred by dietary restriction require pck-2. Together, our results describe a new paradigm in which nutritional signals engage gluconeogenesis to influence aging quality via DAF-16. These data underscore the idea that promotion of gluconeogenesis might be an unappreciated goal for healthy aging and could constitute a novel target for pharmacological interventions that counter high glucose consequences, including diabetes.

It is known that high levels of dietary sugar can negatively impact human health, but the mechanisms underlying this remain unclear. Here we use the facile Caenorhabditis elegans genetic model to extend understanding of the impact of glucose and glucose metabolism on health and aging. We show that the two opposing glucose metabolism pathways–glycolysis and gluconeogenesis–have dramatically opposite effects on health: glycolytic activity responsible for sugar catabolism is detrimental, but driving gluconeogenesis promotes healthy aging. The powerful longevity regulator DAF-16 is required for the healthspan effects of gluconeogenesis. Our data highlight the intriguing possibility that driving the biosynthetic gluconeogenesis pathway could be a novel strategy for healthspan promotion. Indeed, we find that increasing levels of the core gluconeogenic enzyme PEPCK (PCK-2) in just a few intestinal cells can increase overall health in a DAF-16-dependent manner. Dietary restriction, which can promote health and longevity across species, increases PCK-2 levels in the intestine via DAF-16, and PCK-2 is required for the health benefits seen when calories are limited. Our results define gluconeogenic metabolism as a key component of healthy aging, and suggest that interventions that promote gluconeogenesis may help combat the onset of age-related diseases, including diabetes.

Methionine increases yolk production to offset the negative effect of caloric restriction on reproduction without affecting longevity in C. elegans

Caloric restriction (CR) or Dietary restriction (DR) is known to improve health and in many cases increases lifespan. However, its negative effect on reproduction has not been fully studied. Practicing CR/DR without adequate knowledge on its side effect may risk complications such as infertility, birth defect, or malnutrition. In this study, by using several CR strategies in C. elegans, we examine key functions of reproduction including embryonic development and larvae growth. We find that CR significantly decreases the survival of embryos and slows the growth of the offspring. We further determine that defect in oocyte but not sperm is responsible for the compromised reproduction under CR. Interestingly, adding methionine to the medium reverses the reproduction defects, but does not affect the long lifespan resulted from CR. The beneficial effect of methionine on reproduction requires the yolk protein vitellogenin. CR down-regulates vitellogenin expression, which can be reversed by supplementing methionine in the food. Lacking the yolk protein transport due to rme-2 mutation blocks methionine’s beneficial effects. Our study has revealed a novel, methionine-mediated genetic pathway linking nutrient sensing to reproduction and suggested methionine as a potential food supplement to mitigate the side effect of CR.

High-glucose diets induce mitochondrial dysfunction in Caenorhabditis elegans

Glucose is an important nutrient that dictates the development, fertility and lifespan of all organisms. In humans, a deficit in its homeostatic control might lead to hyperglucemia and the development of obesity and type 2 diabetes, which show a decreased ability to respond to and metabolize glucose. Previously, we have reported that high-glucose diets (HGD) induce alterations in triglyceride content, body size, progeny, and the mRNA accumulation of key regulators of carbohydrate and lipid metabolism, and longevity in Caenorhabditis elegans (PLoS ONE 13(7): e0199888). Herein, we show that increasing amounts of glucose in the diet induce the swelling of both mitochondria in germ and muscle cells. Additionally, HGD alter the enzymatic activities of the different respiratory complexes in an intricate pattern. Finally, we observed a downregulation of ceramide synthases (hyl-1 and hyl-2) and antioxidant genes (gcs-1 and gst-4), while mitophagy genes (pink-1 and dct-1) were upregulated, probably as part of a mitohormetic mechanism in response to glucose toxicity.

Evaluation of the effects of three sulfa sweeteners on the lifespan and intestinal fat deposition in C. elegans

High sugar content in beverage or food can affect the aging process, and thus natural/artificial sweeteners are widely used as substitutes. However, whether sweeteners have such adverse effects as sugar remains to be clarified. Therefore, in the current study, three sulfa sweeteners, namely, saccharin sodium salt hydrate (SAC²), sodium cyclamate (CYC³) and acesulfame potassium (AceK⁴) were evaluated for their effects on the lifespan, deposition of lipofuscin, exercise activity, food intake, and intestinal fat deposition (IFD⁵) of Caenorhabditis elegans (C. elegans⁶). It was shown that SAC at 0.3 and 10 mg/mL shortened the lifespan of C. elegans and impaired the exercise capacity, while at other concentrations no significant effects were observed. In contrast, CYC at 0.1, 1 and 10 mg/mL prolonged the lifespan of C. elegans. On the other hand, AceK at 1 mg/mL increased the lifespan of C. elegans, and could decrease both lipofuscin deposition and IFD in a dose-dependent manner. Taken together, these results indicated that although SAC, CYC, and AceK all belong to the sulfa sweeteners, each has distinct effects on different physiological activities associated with aging, at least in C. elegans.

Pomegranate juice and extract extended lifespan and reduced intestinal fat deposition in Caenorhabditis elegans

Pomegranate juice with a high content of polyphenols, pomegranate extract, ellagic acid, and urolithin A, have anti-oxidant and anti-obesity effects in humans. Pomegranate juice extends lifespan of Drosophila melanogaster. Caenorhabditis elegans (C. elegans) (n = 6) compared to the control group in each treatment, lifespan was increased by pomegranate juice in wild type (N2, 56 %, P < 0.001) and daf-16 mutant (daf-16(mgDf50)I) (18 %, P = 0.00012), by pomegranate extract in N2 (28 %, P = 0.00004) and in daf-16(mgDf50)I (10 %, P < 0.05), or by ellagic acid (11 %, P < 0.05). Pomegranate juice reduced intestinal fat deposition (IFD) in C. elegans (n = 10) N2 (-68 %, P = 0.0003) or in the daf-16(mgDf50)I (-33 %, P = 0.0034). The intestinal fat deposition was increased by pomegranate extract in N2 (137 %, P < 0.0138) and in daf-16(mgDf50)I (26 %, P = 0.0225), by ellagic acid in N2 (66 %, P < 0.0001) and in daf-16(mgDf50)I (74 %, P < 0.0001), or by urolithin A in N2 (57 %, P = 0.0039) and in daf-16(mgDf50)I (43 %, P = 0.0001). These effects were partially mediated by the daf-16 pathway. The data may offer insights to human aging and obesity due to homology with C. elegans.

Metabolic shift from glycogen to trehalose promotes lifespan and healthspan in Caenorhabditis elegans

As Western diets continue to include an ever-increasing amount of sugar, there has been a rise in obesity and type 2 diabetes. To avoid metabolic diseases, the body must maintain proper metabolism, even on a high-sugar diet. In both humans and Caenorhabditis elegans, excess sugar (glucose) is stored as glycogen. Here, we find that animals increased stored glycogen as they aged, whereas even young adult animals had increased stored glycogen on a high-sugar diet. Decreasing the amount of glycogen storage by modulating the C. elegans glycogen synthase, gsy-1, a key enzyme in glycogen synthesis, can extend lifespan, prolong healthspan, and limit the detrimental effects of a high-sugar diet. Importantly, limiting glycogen storage leads to a metabolic shift whereby glucose is now stored as trehalose. Two additional means to increase trehalose show similar longevity extension. Increased trehalose is entirely dependent on a functional FOXO transcription factor DAF-16 and autophagy to promote lifespan and healthspan extension. Our results reveal that when glucose is stored as glycogen, it is detrimental, whereas, when stored as trehalose, animals live a longer, healthier life if DAF-16 is functional. Taken together, these results demonstrate that trehalose modulation may be an avenue for combatting high-sugar-diet pathology.

Sexual Dimorphism and Sex Differences in Caenorhabditis elegans Neuronal Development and Behavior

As fundamental features of nearly all animal species, sexual dimorphisms and sex differences have particular relevance for the development and function of the nervous system. The unique advantages of the nematode Caenorhabditis elegans have allowed the neurobiology of sex to be studied at unprecedented scale, linking ultrastructure, molecular genetics, cell biology, development, neural circuit function, and behavior. Sex differences in the C. elegans nervous system encompass prominent anatomical dimorphisms as well as differences in physiology and connectivity. The influence of sex on behavior is just as diverse, with biological sex programming innate sex-specific behaviors and modifying many other aspects of neural circuit function. The study of these differences has provided important insights into mechanisms of neurogenesis, cell fate specification, and differentiation; synaptogenesis and connectivity; principles of circuit function, plasticity, and behavior; social communication; and many other areas of modern neurobiology.

Sex-Specific Gene Expression and Life Span Regulation

Aging-related diseases show a marked sex bias. For example, women live longer than men yet have more Alzheimer's disease and osteoporosis, whereas men have more cancer and Parkinson's disease. Understanding the role of sex will be important in designing interventions and in understanding basic aging mechanisms. Aging also shows sex differences in model organisms. Dietary restriction (DR), reduced insulin/IGF1-like signaling (IIS), and reduced TOR signaling each increase life span preferentially in females in both flies and mice. Maternal transmission of mitochondria to offspring may lead to greater control over mitochondrial functions in females, including greater life span and a larger response to diet. Consistent with this idea, males show greater loss of mitochondrial gene expression with age.

Lipid and Carbohydrate Metabolism in Caenorhabditis elegans

Lipid and carbohydrate metabolism are highly conserved processes that affect nearly all aspects of organismal biology. Caenorhabditis elegans eat bacteria, which consist of lipids, carbohydrates, and proteins that are broken down during digestion into fatty acids, simple sugars, and amino acid precursors. With these nutrients, C. elegans synthesizes a wide range of metabolites that are required for development and behavior. In this review, we outline lipid and carbohydrate structures as well as biosynthesis and breakdown pathways that have been characterized in C. elegans We bring attention to functional studies using mutant strains that reveal physiological roles for specific lipids and carbohydrates during development, aging, and adaptation to changing environmental conditions.

Sex-specific lifespan and its evolution in nematodes

Differences between sexes of the same species in lifespan and aging rate are widespread. While the proximal and evolutionary causes of aging are well researched, the factors that contribute to sex differences in these traits have been less studied. The striking diversity of nematodes provides ample opportunity to study variation in sex-specific lifespan patterns associated with shifts in life history and mating strategy. Although the plasticity of these sex differences will make it challenging to generalize from invertebrate to vertebrate systems, studies in nematodes have enabled empirical evaluation of predictions regarding the evolution of lifespan. These studies have highlighted how natural and sexual selection can generate divergent patterns of lifespan if the sexes are subject to different rates or sources of mortality, or if trade-offs between complex traits and longevity are resolved differently in each sex. Here, we integrate evidence derived mainly from nematodes that addresses the molecular and evolutionary basis of sex-specific aging and lifespan. Ultimately, we hope to generate a clearer picture of current knowledge in this area, and also highlight the limitations of our understanding.

Chronic hyperglycemia affects bone metabolism in adult zebrafish scale model

Type II diabetes mellitus is a metabolic disease characterized by chronic hyperglycemia that induce other pathologies including diabetic retinopathy and bone disease. The mechanisms implicated in bone alterations induced by type II diabetes mellitus have been debated for years and are not yet clear because there are other factors involved that hide bone mineral density alterations. Despite this, it is well known that chronic hyperglycemia affects bone health causing fragility, mechanical strength reduction and increased propensity of fractures because of impaired bone matrix microstructure and aberrant bone cells function. Adult Danio rerio (zebrafish) represents a powerful model to study glucose and bone metabolism. Then, the aim of this study was to evaluate bone effects of chronic hyperglycemia in a new type II diabetes mellitus zebrafish model created by glucose administration in the water. Fish blood glucose levels have been monitored in time course experiments and basal glycemia was found increased. After 1 month treatment, the morphology of the retinal blood vessels showed abnormalities resembling to the human diabetic retinopathy. The adult bone metabolism has been evaluated in fish using the scales as read-out system. The scales of glucose-treated fish didn't depose new mineralized matrix and shown bone resorption lacunae associated with an intense osteoclast activity. In addition, hyperglycemic fish scales have shown a significant decrease of alkaline phosphatase activity and increase of tartrate-resistant acid phosphatase activity, in association with alterations in other bone-specific markers. These data indicates an imbalance in bone metabolism, which leads to the osteoporotic-like phenotype visualized through scale mineral matrix staining. The zebrafish model of hyperglycemic damage can contribute to elucidate in vivo the molecular mechanisms of metabolic changes, which influence the bone tissues regulation in human diabetic patients.

Glucose or Altered Ceramide Biosynthesis Mediate Oxygen Deprivation Sensitivity Through Novel Pathways Revealed by Transcriptome Analysis in Caenorhabditis elegans

Individuals with type 2 diabetes display metabolic abnormalities, such as hyperglycemia, increased free fatty acids, insulin resistance, and altered ceramide levels, that contribute to vascular dysfunctions and compromised oxygen delivery. Caenorhabditis elegans fed a glucose-supplemented diet or with altered ceramide metabolism, due to a hyl-2 mutation, are sensitive to oxygen deprivation (anoxia). Our experiments showed that the combination of these factors further decreased the anoxia survival. RNA-sequencing analysis was performed to assess how a glucose-supplemented diet and/or a hyl-2 mutation altered the transcriptome. Comparison analysis of transcripts associated with anoxia-sensitive animals [hyl-2(tm2031) mutation or a glucose diet] revealed 199 common transcripts encoded by genes with known or predicted functions involving innate immunity, cuticle function (collagens), or xenobiotic and endobiotic phase I and II detoxification system. Use of RNA interference (RNAi) to target gene products of the xenobiotic and endobiotic phase I and II detoxification system (UDP-glycosyltransferase and Cytochrome p450 genes; ugt-15, ugt-18, ugt-19, ugt-41, ugt-63, cyp-13A12, cyp-25A1, and cyp-33C8) increased anoxia survival in wild-type animals fed a standard diet. Anoxia sensitivity of the hyl-2(tm2031) animals was suppressed by RNAi of cyp-25A1 or cyp-33C8 genes. A glucose diet fed to the P0 hermaphrodite decreased the anoxia survival of its F1 embryos; however, the RNAi of ugt-63 and cyp-33C8 suppressed anoxia sensitivity. These studies provide evidence that the detoxification system impacts oxygen deprivation responses and that C. elegans can be used to model the conserved detoxification system.